1. Field of the Invention
The present invention relates to a photoacoustic measurement device, and more particularly, to a photoacoustic measurement device that detects photoacoustic waves generated in a subject after light is emitted to the subject. In addition, the invention relates to a laser light source used in the photoacoustic measurement device.
2. Description of the Related Art
An ultrasonic inspection method has been known as a kind of an image inspection method which can non-invasively inspect the inside of a living body. In ultrasonic inspection, a probe which can transmit and receive ultrasonic waves is used. When ultrasonic waves are transmitted from the probe to the subject (living body), the ultrasonic waves are propagated through the living body and are reflected from a tissue interface. The probe receives the reflected sound waves and a distance is calculated on the basis of the time required for the reflected ultrasonic waves to return to the probe. In this way, it is possible to image the internal structure of the living body.
In addition, photoacoustic imaging has been known which images the inside of a living body using a photoacoustic effect. In general, in this photoacoustic imaging, the living body is irradiated with pulsed laser light. In the inside of the living body, the tissue of the living body absorbs the energy of the pulsed laser light and ultrasonic waves (photoacoustic signal) are generated by adiabatic expansion caused by the energy. The photoacoustic signal is detected by, for example, a probe and a photoacoustic image is formed on the basis of the detected signal. It is possible to visualize the inside of the living body on the basis of the photoacoustic signal.
In the photoacoustic imaging, in many cases, a Q switch laser is used as a light source for emitting pulsed laser light. In the Q switch laser, a Q switch for controlling optical loss is provided in an optical resonator. For example, a Pockels cell is used as the Q switch. Until a laser medium is sufficiently excited, the Q switch is turned off to increase the loss of the optical resonator, thereby suppressing oscillation. When the Q switch is switched from the off state to an on state after the laser medium is sufficiently excited, a sufficient amount of stored energy oscillates at one time and a giant pulse which has very high intensity and a short pulse width is obtained. The Q switch returns to the off state after the pulsed laser light is emitted.
For example, JP2011-224205A discloses a photoacoustic image generation device using a Q switch laser. In JP2011-224205A, plates for pressing a subject, a detector for detecting photoacoustic waves, and a Q switch laser serving as a light source are provided in an exterior cover for shielding light. A door for manual operation is provided in the exterior cover. An operator, such as a doctor, puts a hand through the door for manual operation and interposes the subject between the plates. After the subject is interposed between the plates, light is radiated to the subject and photoacoustic waves generated in the subject are detected.
In addition, JP2011-224205A discloses a structure in which, when the door for manual operation is opened, it is determined whether to stop the emission of light from the Q switch laser or to shield laser light. When a door opening and closing detection sensor detects that the door for manual operation is opened, a control unit turns off the Q switch of the Q switch laser. In addition, the control unit closes a shutter which is provided on the optical path of the laser light such that the laser light emitted from the Q switch laser is not radiated to the subject. JP2011-224205A also discloses that it is preferable to turn off the Q switch and to close the shutter in order to further improve safety.